Sen. Chuck Schumer is sell ing his home state down the river in his quest to replace Sen. Harry Reid as Senate Majority Leader. But will anyone make him pay a price for it?

Despite his reliably liberal voting record in his almost 30 years in Congress, Schumer has cast himself as the defender of the middle class on economic and tax issues. And he aggressively advocated for his constituents, be they dairy or fruit farmers, manufacturers or local governments.

He also protects Wall Street from the more populist impulses of his party — albeit while shaking down campaign contributions from the barons of banking, finance and insurance. Indeed, he used those contacts to great success as head of the Senate Democratic Campaign Committee in 2006 and 2008, helping his party win a filibuster-proof majority in the Senate.

Even those of us who never much liked Schumer’s policy positions had to admire his political skill. But something has changed: In his quest to replace Reid after his likely loss in Nevada this November, Schumer has abandoned the interests of his state.

When President Obama and Attorney General Eric Holder decided to bring al Qaeda terrorists to New York City for federal court trial, exposing the city anew as a terrorist target and costing taxpayers hundreds of millions of dollars, Schumer didn’t utter a word of objection. Imagine his outrage if President George W. Bush had made that decision.

But there is no greater example of Schumer abandoning New Yorkers’ interests than his actions over the health-care legislation. Both Gov. Paterson and Mayor Bloomberg have called the Senate-passed bill a disaster for our financially strapped state: It would add more than $1 billion in Medicaid costs to state and local governments.

Schumer testily disputes this critique but offers no substantive defense of the bill that he supports. For example, when newly elected Westchester County Executive Rob Astorino warned that higher Medicaid costs would be borne by property-tax payers, Schumer airily dismissed him as being “wrong.”

Who are we to believe: the state and local officials who’ve studied the bill and who’ll be responsible for finding the money to pay for it — or Schumer?

Then there are the legislative bribes that Reid and Schumer arranged to buy votes to pass the Senate bill: Nebraska is exempted from higher Medicaid costs; Louisiana gets a special $300 million kiss; Florida seniors won’t be subjected to cuts in popular Medicare Advantage programs. For New York, Schumer delivered bupkis.

And, as the Empire State gets hosed under Senate and House health bills with higher taxes to pay for goodies for other states, Schumer does his utmost to protect his servile counterpart, appointed Sen. Kirsten Gillibrand, from political competition — elbowing out at least five serious contenders away from a primary challenge. Last week, news accounts had him warning a new potential rival, former Tennessee Rep. Harold Ford, away from a race.

All this activity actually holds risk for Schumer: He has to run for re-election this year. And if New Yorkers wise up to what their senior senator has been doing to them, they won’t be pleased.

Blinded by ambition and arrogance, he has left himself vulnerable to a serious challenge — if only the GOP and Conservative Party establishments will open their eyes. Indeed, Schumer’s image of invincibility has been fed by the failure of Republicans in New York and Washington to aggressively attack his vulnerabilities.

But the old expression holds: “The bigger they are, the harder they fall.” His higher — and increasingly negative — national profile could generate substantial contributions from across the country for a promising challenger.

So, despite his huge campaign war chest, Schumer is actually ripe for the taking — if some enterprising and fearless Republican candidate decides to take on this mission. New Yorkers don’t like to be sold a bill of goods, and they especially don’t like being sold down the river.

John Faso, the 2006 GOP candidate for governor, is a co-founder of New Yorkers for Growth.